Heather L. Horst was like a sister to Aaron W. Allen, so when she said her husband was abusive and the only way she could escape was if he was dead, Allen helped plan his shooting, according to charges filed Monday.

Horst, 24, and Allen, 25, of South St. Paul, were charged Monday with second-degree murder and conspiracy to commit a felony for the death of her husband, Brandon J. Horst, 25, a St. Paul National Guardsman.

Brandon Horst was found unresponsive on Aug. 5 in the home the couple shared on the 400 block of Bellows Street on the city’s West Side.

According to charges:

Shortly after 1 a.m. on Aug. 5, Heather Horst called 911 and reported that her husband was in bed with a lot of blood coming from his head. She said she did not know what happened. Authorities found Brandon Horst in the upstairs bedroom with a single gunshot wound to the head. A single 9mm casing was also found on the bed.

Officers searched the house, which was dirty and filled with garbage, but there were no signs that it had been ransacked. Heather Horst told police she and her husband had been arguing for days about having an open relationship. The couple each had other partners lined up. Heather Horst told police her marriage was tumultuous and that her husband had assaulted her before. She said they argued before Brandon Horst went to work at 2 p.m. on Aug. 4.

Heather Horst’s friend, who is Brandon Horst’s stepsister and Allen’s fiancée, initially corroborated a version of that story, but she admitted to police on Aug. 9 what happened.

She said that Heather Horst came to the apartment that she shared with Allen and said, “I want him dead.” She explained that they had been arguing a lot over the past few days. Heather Horst told Allen that she wanted to make it look like someone broke into the house.

Allen’s fiancée said she didn’t think Heather Horst was serious, but around 10:30 p.m. on Aug. 4, Heather Horst picked up Allen and went to the Horst home. Heather Horst left Allen there and drove to pick up her friend at her apartment.

Heather Horst told Allen’s fiancée that she left her gun for Allen on the dining room table, and Allen then waited in the basement for Brandon Horst to fall asleep. Allen told her that he shot Brandon Horst in the head.

They picked up Allen a block away from the home with a black backpack, which he dropped off near the Frisbee golf area at Kaposia Park in South St. Paul. When police later recovered the backpack, they found a 9mm handgun and a box of ammunition inside.

She also told police that Heather Horst learned she was pregnant about two weeks before and was not happy about it.

Police recovered five text messages between Heather Horst and Allen that had been made shortly after midnight on August 5 and then deleted from her phone:

At 12:17 a.m., Allen texted Heather Horst, “And tyler [one of the Horsts’ dogs] won’t shut up there is a TV on upstairs.”

Officers also spoke to a roommate who lives with Allen and his fiancée who said Heather Horst came over to their apartment on Aug. 4 upset over having lost a baby. She, Allen and his fiancée talked inside a bedroom. The roommate later heard Heather Horst say her husband abused her and the only way she could leave their marriage or be free from him was if he was dead.

The roommate told police that Allen came home out of breath around 1 a.m. on Aug. 5. He later heard Heather Horst talk about a life insurance policy and that she was going to give them some money for it forhis help.

Brandon Horst had a military life insurance policy in the amount of $400,000. He had another $80,000 life insurance policy from the federal government because of his position as a federal technician. Heather Horst was the sole beneficiary of these policies.

Allen’s fiancée said she was afraid to tell police the truth because she was afraid of losing her fiancé.

Test results showed that the casing found by Brandon Horst’s body had been fired by the same weapon that fired the casing in a gun case owned by Heather Horst.

The Minnesota National Guard said that Horst has worked full-time at the 133rd Airlift Wing for nearly the past two years, was a member of the Wing for six years and recently re-enlisted. During his initial enlistment, he deployed to Southwest Asia for approximately six months.